San Salvador , El Salvador -LRB- CNN -RRB- -- Buried underground about 30 miles from El Salvador 's capital city , police made a staggering find this week : 213 grenades .

Investigators described the arsenal uncovered Tuesday as `` anti-tank grenades '' -- the kind of weapons only members of the military are allowed to use in the Central American country .

Key questions remain after the discovery : Who hid the grenades there ? And how were they planning to use them ?

Authorities say they suspect the stash is yet another sign that Mexico 's brutal Zetas cartel has extended its reach . And members of the military could be involved , they said .

`` According to our investigations , these have been sold to Zetas drug traffickers in Guatemala and Mexico , '' Salvadoran Attorney General Luis Martinez told reporters . `` And we are going to investigate this . And also we are going to see where they came from . ''

Authorities have asked the United States for assistance with their investigation into the weapons ' origin .

Police said the grenades , buried about 4 feet underground , were manufactured in China and the United States .

Los Zetas known for ` complete absence of scruples '

CNN 's Catherine E. Shoichet contributed to this report .

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Police say they found 213 anti-tank grenades buried underground

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They suspect the stash is connected with a cartel , possibly Mexico 's Zetas

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The grenades were manufactured in China and the United States , police say